Since materials having a two-dimensional structure not only facilitate a synthesis of relatively complicated structures but also is relatively easy to change the properties of the materials, extensive studies thereon have been conducted. Recently, among the materials having a two-dimensional structure, graphene is a one of the materials that have gained the most attention.
Graphene is a semi-metallic material where carbon atoms form an arrangement connected in a hexagonal shape by two-dimensional sp2 bonding while having a thickness corresponding to a carbon atom layer, and has the properties of structural and chemical stability and excellent thermal conductivity. In addition, graphene is consisting of only carbon which is a relatively light element, and thus, easy to be processed in one-dimensional or two-dimensional nano-patterns.
Meanwhile, graphene is highly likely to be used as an electromagnetic wave absorber. In this regard, there are several things that need to be improved. First, since graphene is a non-magnetic material, there is a limitation that it can only absorb microwave energy. In addition, graphene has the disadvantage of having poor impedance matching because the dielectric permittivity and magnetic permeability are not in balance.
As an alternative thereto, a method of introducing a magnetic material onto the surface of graphene has been proposed. However, in the conventionally known method, graphene is prepared from graphite or the like, and then a magnetic material is introduced onto the surface of graphene. In other words, the preparation process of graphene and the introduction process of magnetic materials are divided. Accordingly, it is difficult to uniformly introduce a magnetic material onto the surface of graphene, and there is a high possibility of causing defects on the surface of graphene during the process of introducing a magnetic material.
Meanwhile, various methods for preparing graphene have been reported so far. First, there is a method for preparing graphene by chemical vapor deposition (CVD), which has the advantage of enabling the preparation of high quality graphene, but it is not suitable for mass production due to limited production speed. A method wherein a graphene sheet is exfoliated from graphite by a physical method such as using a tape, is known. However, this method is also not suitable for mass production and has the disadvantage of having a very low exfoliation yield.
Further, there is a method of oxidizing graphite to proceed an exfoliation and reducing the graphene oxide obtained therefrom to obtain graphene. However, there are disadvantages in that toxic substances must be used and that it is difficult to control the defects of graphene.
Accordingly, the present inventors have conducted extensive and intensive studies on a simple and effective method of introducing a magnetic material onto the surface of a graphene, and found that magnetic particles in the form of FeOx are naturally formed by employing a method of preparing graphene from a graphite intercalation compound (GIC) described later, wherein a halogen salt of iron is used as an intercalant, thereby completing the present invention.